One of the most common natural monomers is glucose, a simple carbohydrate.
A monomer is a repeating structure or unit within a type of large molecule known as a polymer. The word comes from the Greek mono, which means one, and mere, which means part; it is one of many similar parts of a long chain that makes up the molecule. Monomers join together to form polymers during a chemical reaction called polymerization, where molecules come together by sharing electrons in what is called a covalent bond. They can also join together to form smaller structures: a dimer is made up of two monomers and a trimer is made up of three, for example. Polymers can consist of many thousands of these units.
The structural properties of a polymer depend on the arrangement of the monomers that compose it. This can affect its water solubility, melting point, chemical reactivity, or durability. Two polymers can contain the same monomer molecules, but due to their arrangement, they can have different properties.
Unit
A key characteristic of a monomer unit is its ability to bind at least two other molecules. The number of molecules that a unit is capable of binding is determined by the number of active sites where covalent bonds can form. If you can only attach two other molecules, they will form chain-like structures. If you can connect with three or more monomers, more advanced three-dimensional crosslinked polymers can be built. The element carbon forms the basis of most polymers, as it is one of the few elements that can bond in four different directions with four other atoms.
The joining process does not necessarily involve two monomeric units simply joined. In many cases, each unit loses one or two atoms, which form another product. For example, one unit can give up a hydrogen atom and the other a hydroxyl group, or hydrogen-oxygen, to form a bond, producing water (H2O) as a byproduct. This type of polymerization is known as a condensation reaction.
polymer types
A polymer that consists entirely of one type of monomeric unit is called a homopolymer. If there is more than one type of unit, it is known as a copolymer. They can be grouped into different categories depending on how the units are organized:
Alternating: two different units alternate, for example… ABABAB… Periodic: a given sequence of units repeats, for example… ABCABCABC… Block: two or more different homopolymers are bonded together, for example … AAAABBBB… Statistical: the sequence of units has no fixed pattern, but certain combinations are more likely than others Random: the sequence has no discernible pattern
natural monomers
One of the most common natural monomers is glucose, a simple carbohydrate. It can join other glucose molecules in a variety of ways to form many different polymers. Cellulose, found in the cell walls of plants, consists of chains of glucose molecules up to 10,000 or more units in length, giving it a fibrous structure. In starch, glucose units form branched chains. The many branch ends form points at which enzymes can begin to break down the molecule, making it more easily digestible than cellulose.
Other examples are amino acids, which can join together to form proteins, and nucleotides, which can polymerize together with certain carbohydrate compounds to form DNA and RNA, the molecules on which all known life is based. Isoprene, a hydrocarbon compound found in many plants, can polymerize into natural rubber. The elasticity of this substance is due to the fact that the units form coiled chains that can be stretched and that contract back to a coiled state when released.
synthetic polymers
Many synthetic polymers have been produced and include everyday materials such as plastics and adhesives. Often the monomers from which they are built are natural compounds, although they can often be produced synthetically. In most cases, these compounds are hydrocarbons, molecules that contain only carbon and hydrogen.
An example is ethylene (C 2 H 4 ), a simple hydrocarbon produced by plants but manufactured on a large scale from petroleum. It can polymerize to form polyethylene, sometimes called polyethylene, the most widely used plastic. In essence, it is done by converting the double bond between the two carbon atoms of ethylene into a single bond, allowing each one to be able to form another single bond with a neighboring carbon atom and allowing the formation of long chains. Other examples are propylene and styrene, which are used in the manufacture of polypropylene and polystyrene, respectively.